Process for the manufacture of light colored surface-active sulfo fatty acid esters



June 24, 1969 w. STEIN ET AL 3,452,064

PROCESS FOR THE MANUFACTURE OF LIGHT COLORED SURFACE-ACTIVE SULFO FATTY ACID ESTERS Filed Jan. 11, 1965 INVENTORS WERNER STEIN HERBERT WEISS OTTO KOCH finite ABSTRACT OF THE DISCLOSURE There is disclosed an improved process for bleaching sulfo fatty acid esters. When the known process, i.e. hydrogen peroxide bleaching of sulfonic acids obtained by reacting fatty acid esters in the absence of solvents with a gaseous sul-fur trioxide-inert gas mixture is attempted, particularly when it is attempted to carry Out the bleaching process continuously, on addition of a hydrogen peroxide to the sulfonic acids, an inhomogeneous lumpy almost impossible to mix and/or pump, mass is obtained. Because of the resultant irregular distribution of the hydrogen peroxide, localized overheating takes place and colored contaminants are formed. The applicants process avoids the latter disadvantages by teaching that the bleaching agent, i.e. hydrogen peroxide, is to be added in an amount of at most 4% by weight of the sulfonic acids which should have been preheated to 45 C. and the bleaching of the mixture effected at a temperature not exceeding 100 C. The resulting mixture is then neutralized by addition of a neutralizing agent to produce a pH of 4, thereafter additional bleaching agent is added, and the bleaching completed. Thus there is involved a twostage bleaching procedure, a light-to-substantially colorless product being ensured in each instance.

This invention relates to a method of manufacturing light colored surface-active sulfo fatty acid esters and the products produced by such a process. More specifically, this invention relates to a method for bleaching such fatty acids with hydrogen peroxide and the like.

United States Patent 3,159,657 describes a process for bleaching sulfo fatty acid esters, which consists of hydrogen peroxide bleaching of sulfonic acids obtained by treating fatty acid esters, in the absence of solvents and in absence of substances being able to form adducts With sulfur trioxide, with gaseous sulfur trioxide diluted with inert gas. Furthermore, United States Patent No. 3,142,691 discloses that hydrogen peroxide can be replaced in this process by substances which form hydrogen peroxide, or by a number of other inorganic bleaches. United States application 194,997 filed May 15, 1962, abandoned in favor of United States application 434,683, filed Feb. 23, 1965, now patent No. 3,354,187 describes another improvement of this process, which consists first in partially bleaching the sulfonation product in the acid state, and then, after a thorough neutralization of the sulfonation product, continuing the bleaching process.

In an attempt to reduce this bleaching process to commercial practice technical difficulties occurred whenever the percentage of sulfo fatty acid esters with 16 to 22 carbon atoms, and preferably with 16 to 20 carbon atoms, amounted to more than 70% and preferably more than 85% of the total fatty acid esters. The fatty acid radicals of such esters of sulfo fatty acids or sulfo fatty acid States Patent G 3,452,064 Patented June 24, 1969 mixtures can consist preferably of more than 90% C and C fatty acid radicals, which is the case, for example, with sulfo fatty acid esters made from hydrogenated tallow fatty acid.

According to the applicants findings, such sulfonic acids, when processed in continuous apparatus, have to be kept at temperatures of at least 45 C., and preferably of at least 50 C., in order to remain fluid, because of their high melting or softening point. When the amount of hydrogen peroxide necessary for bleaching is added, the originally viscous, though substantially homogeneous mass turns lumpy and becomes an inhomogeneous product that is very hard to mix and is practically impossible to pump. On account of the irregular distribution of the hydrogen peroxide, local overheating is produced by the exothermic bleaching reaction that takes place immediately, and colored contaminants are formed.

It is therefore an object of this invention to overcome these and other difiiculties encountered in the prior art. More specifically, it is an object of this invention to bleach sulfonic acids in such a manner so as to substantially obviate the difiiculties encountered in which the sulfonic acids turn lumpy and inhomogeneous during bleaching and consequently hard to mix, and pump. It is a further object of this invention to provide a regular distribution of hydrogen peroxide in sulfonic acid compositions being bleached to avoid local overheating produced by the exothermic bleaching reaction and to avoid colored contaminants formed during such overheating.

These and other objects have been achieved by the method of this invention in which:

The figure of the accompanying drawing relates to apparatus for continuously bleaching a sulfonic acid.

It has now been found that even sulfonation products such as these can be bleached continuously in a technically easy to perform process if a liquid bleaching agent in a quantity of at most 4% H 0 (the other bleaching agents are to be used in an amount equivalent tothis amount of H 0 of the weight of the sulfonation product is added to the sulfonation product after the latter has been heated to at least 45 C., the bleaching is performed at temperatures not above 100 C. and preferably not above 90 C. and especially not above C., then adding neutralizing agents until a pH value of 4 is achieved, after which the bleaching agent is then added again.

The sulfo fatty acid esters to be processed according to the invention are the derivatives of alpha sulfo fatty acids known in the art, comprising esters which may be derived from monovalent aliphatic alcohols with 1 to- 4 carbon atoms or from polyvalent alcohols, especially from glycerine. At the same time, the starting materials to be sulfonated are not to contain, other than the hydrogen atoms on the alpha carbon atom of the fatty acid radical, any additional sulfonatable or sulfatable groups, and especially they are not to contain any double bonds or alcoholic hydroxyl groups. The fatty acid radicals are to be highly saturated, i.e., they are to have an iodine number of less than 5 and preferably of less than 2 and especially less than 1.

For sulfonation, the fatty acid esters, which are practically undiluted with solvents, are treated with gaseous S0 in a quantity of 1.1 to 1.7, and preferably 1.2 to 1.5 mols per mol of fatty acid radical, the entire amount of S0 required for the sulfonation being made to Work at least for a time at temperatures above 70 C. In this manner, sulfonation products are obtained :with a degree of sulfonation of at least preferably at least 94%, and especially of approximately 96%.

The minimum temperatures to be maintained in the first bleaching stage to liquefy the sulfonate depend to some extent on the fatty acid composition. If fatty acid radicals are present in quantities of about 30% by weight, which have a maximum of 14 carbon atoms and especially if they have 10 and 12 carbon atoms, the sulfonation product softens at about 45 C. and can be worked in continuous apparatus at this temperature. As the carbon number of the fatty acid radicals increases, the minimum temperatures also increase. A sulfonic acid whose fatty acid radicals consist of at least 90% C and/or C fatty acid radicals, such as one made from hydrogenated tallow fatty acid ester, it is advantageous to work at temperatures of at least 50 C., and preferably of at least 55 C. The temperature of the sulfonic acid paste before the addition of the bleaching agent is not to exceed 70 C. if possible, and preferably it should not exceed 65 C.

The bleaching agent is used in the form of a 10 to 70%, and preferably 15 to 60%, solution or suspension. If suspensions of undissolved bleaching agents are used, their concentration ought not to exceed 45 wt. percent and preferably it ought not to exceed 35 wt. percent.

Instead of hydrogen peroxide, substances can also be used which form hydrogen peroxide under the conditions of the reaction; these include the salts or hydroperoxides of hydrogen peroxide known in the art, or compounds formed thereof by addition to organic substances. Chlorites, chlorates and perchlorates and the corresponding free acids or their anhydrides can also be used as bleaches, in which case their quantity is to be equivalent to the above-stated amount of hydrogen peroxide.

As cationic component there may be present in all these bleaching agents alkali metal cations as sodium, potassium, lithium and others, ammonium, earth alkali cations as magnesium, calcium, barium, strontium as well as amines or alkylol-amines containing l-8, preferably 1-6 C-atoms per molecule.

All these bleaches are to be used preferably in the presence of so much water that, according to calculations, a mixture forming from the excess S present in the sulfonic acid and the water that is added consists of 30 to 90 wt. percent, and preferably 40 to 85 wt. percent, of sulfur trioxide. These values relate to the amounts of sulfur trioxide and water present before the commencement of the bleaching. If SO -binding components are present in the bleaches (cations of salts), the amounts of 80;, that are consumed (by salt formation) do not enter into the computation.

Inorganic or orgnaic bases, as for example the carbonates or bicarbonates that are derived from ammonium, sodium, potassium, magnesium or low organic amines or alkylolamines with 1 to 6 carbon atoms in the molecule, can be used as neutralizing agents. Mono, di or triethanolamine are to be preferred among the amines for such use. The neutralizing agents can be used in the form of aqueous solutions in concentrations of 1 to 30 wt. percent and preferably 3 to 20 wt. percent. If the neutralizing agents are liquids themselves (e.g., the abovenamed alkylolamines), they can also be used as they are, i.e., not in the form of aqueous solutions.

The pH value of about 4 which is to be adjusted prior to beginning the second bleaching stage corresponds to a neutralization of about 75% of the total sulfonic acid. It is possible, however, to neutralize extensively, to a pH value, for example, of at least 5 or at least 6. In the second bleaching stage the bleaching effect depends to a great extent on the pH value, so that pH values of as much as 11, for example, can be adjusted. However, it is preferable to neutralize to a pH in the neutral range, such as from 6 to 8.

The bleaching agent to be used in the second stage can be added together with the neutralizing agent or following the latter. Not all of the bleaches that can be used in an acid medium can be used equally well in the second bleaching stages; hydrogen peroxide or compounds which form hydrogen peroxide under the bleaching conditions are the most important, and also hypochlorous acid or salts thereof.

If hypochlorous acid or its salts are used, it is recommendable to perform the bleaching at temperatures from 10 to 70 C. and preferably 20 to 60 C. If hydrogen peroxide is used, it is recommended to bleach at elevated temperatures ranging, say, from 50 to 100 C. and preferably 50 to C.

The amount of the oxidant to be used in the second bleaching stage can be just as great as was used in the first stage; it can also be greater, however, and may range from 2 to 6 wt. percent of H 0 or equivalent amounts of other bleaching agents.

It may happen that the bleaching agent used in the first stage has not yet been fully used up at the time of the neurtalization. If a different bleaching agent is used in the second bleaching stage, which reacts with the bleaching agent of the first stage to produce a mutual oxidation or reduction, the bleaching agent of the second stage is to be used in a correspondingly larger amount.

The duration of the second bleaching stage may vary within wide limits. The minimum bleaching time depends, of course, on the sulfonate concentration, the amount and nature of the bleaching agent used, and the bleaching temperature. In general it should be from 5 to 10 minutes. Indeed, the duration of the second bleaching stage may be as long as desired. Practically speaking, the timing of the second bleaching stage is probably of no great importance, because the sulfonic acid with the neutralizing and bleaching agents added is usually transferred into tanks. A tank of this sort also serves, particularly in industrial production, as a storage tank in which the material with the bleach added is let stand, so that the bleaching takes :place in the tank Without further ado, in the course, for example, of 12 or 24 hours.

The above-described bleaching process is especially suited for continuous performance. An apparatus such as the one shown in the annexed drawing can be used, for example, for this purpose. Supply tanks 1, 2, 3 and 4 con tain the sulfonation product that is to be bleached, the bleaching agent for the first stage, the bleaching agent for the second stage and the neutralizing agent respectively. The sulfonation product and the first-stage bleach are fed throgh the proportioning pumps 5 and 6 via conduits 25 and 26 to a mixing apparatus 9. The sulfonation product, mixed with bleaching agent, passes through 29 to the heat exchanger 10 and, advantageously, through a temperature-controlled tank 11, to a second mixer 12, into which neutralizing agent and second-stage bleaching agent are fed by the proportioning pumps 7 and 8 through conduits 27 and 28. It is advantageous to feed a portion of the sulfonation product with first-stage bleaching agent added back to the mixer 9, the ratio between the quantity of partially bleached feedback and the quantity of unbleached sulfonate being able to range from 9:1 to 121 and preferably from 5:1 to 2:1.

The sulfonation product with bleaching agent added can be fed back to the mixer 9 either after it leaves the heat exchanger 10 through valve 32 and conduit 33 or after it leaves the tank 11 and is passed through valve 34, conduit 33 and pump 13. The product coming from the second mixer 12 passes through conduit 24 into tank 14 equipped with a stirrer 22, the dimensions of the tank being such as to result in a time of stay that is sufficient for the second-stage bleaching operation.

The behavior which is responsible for the technical difficulties explained in the beginning, and which occur when hydrogen peroxide is worked into sulfonic acids of the nature of the sulfonated hydrogenated tallow fatty acid esters, has not been previously described. Therefore, one skilled in the art has been unable to learn, from the state of the art, how sulfonic acids of this kind can be bleached by a technically usable procedure.

The following non-limiting examples are given as certain preferred embodiments of the invention and are not to be construed as narrowing the novel method and composition of the inventors.

Example 1 A sulfonation product made of hardened tallow fatty acid methyl ester (Iodine No. 0.3) was used as the starting material, which had been made according to the teaching in US. patent application Ser. No. 194,840 filed May 15, 1962, issued to US. Patent 3,256,303 on June 14, 1966, by stepwise sulfonation with gaseous sulfur trioxide diluted with inert gas, at increasing temperatures, the product to be sulfonated being finally obtained at temperatures of 75 to 85 C. The sulfonation degree of the product amounted to 95% and contained 7% free S Bleaching this sulfonation product required the addition of approximately 3.5% by Weight, of H 0 When this amount is added as a 40% aqueous solution, it stiffens to a solid mass. It is true that this stiffening can be prevented by heating the sulfonation product to 75 to 80 C. before adding the hydrogen peroxide, but the strongly exothermic reaction can then no longer be controlled, and dark colored decomposition products form while the temperature rises to more than 100 C.

The sulfonation product can nevertheless be bleached continuously in the apparatus described and shown in the figure in the following manner, all quantities relating to the weights put through per hour. 2,660 grams of the sulfonation product were mixed in mixer 9, after cooling to 50 C., with 105 grams of 40% hydrogen peroxide (sulfur trioxide content of the hypothetical mixture of sulfur trioxide and water=70 wt. percent). Most of the heat of reaction was removed in heat exchanger 10, so that the partially bleached product left the heat exchanger at a temperature of 55 C. It then passed into intermediate tank 11, where it was heated within minutes to 60 C., and after leaving the tank it was neutralized with 6.5% caustic soda solution. The paste thus obtained was then thinned at a temperature of 45 C. with 5 wt. percent (with reference to the wash-active substance in the paste) of an aqueous solution containing 13 wt. percent of NaOCl, and pumped from there into the accumulation tank 14. The following color values were read from neutralized solutions containing 5 wt. percent of Washactive substance in a 4" cell in the Lovibond tintometer:

The starting material was the sulfonation product of a mixture having an Iodine number of 0.2 comprising 80% of a methyl ester of a hardened tallow fatty acid and of a methyl ester of a hardened coconut fatty acid. The sulfonation product, which had been made in a manner similar to that described in Example 1, and which contained 7 wt. percent of excess S0 was cooled to 50 C. and bleached in the following manner in the above-described apparatus also shown in the figure, all quantities mentioned referring to the hourly throughput. Two thousand and sixty grams of the sulfonation product were combined in mixer 9 with 105 grams of 40% hydrogen peroxide (sulfur trioxide content of the hypothetical mixture of sulfur trioxide and water=70 wt. percent). A partial flow of the sulfonation product, cooled and with bleaching agent added to it, also was pumped into the mixer, this partial flow amounting approximately to 2.5 times the introduced mixture of sulfonation product and hydrogen peroxide. By varying this mixture ratio the temperature of the product coming from the mixer was kept to 80 to 85 C. The product then passed into the heat exchanger 10, in which it was cooled to 60 C. A por tion of the product coming from the heat exchanger was fed back to the mixer 9; the rest ran through the intermediate tank 11, where it was kept for 10 minutes at 60 C. The product coming from there was neutralized with a 6.5% caustic soda solution and then 5 wt. percent (with reference to the wash-active substance present in the sulfonate paste) of an aqueous solution containing 13 wt. percent of NaOCl. Then the paste went into a heatable tank in which it was kept for 3 hours at 50 C.

The color values of solutions containing 5% washactive substance were determined immediately after neutralization, in one case, and after the bleaching had ended in the other, in a 4" cell in the Lovibond tintometer. These color values were:

The exact structure of the bleached sulfonated fatty acids obtained is not known except in terms of physical properties and the approximate or general nature of the starting materials employed. The method of manufacturing such sulfonated fatty acids and its bleached counterpart however may be held to extremely close physical limits, thereby permitting duplication of the product of this invention from reaction to reaction.

Thus there has been described a novel bleaching process and product obtained thereby wherein an acid sulfonation product is bleached in a first stage followed by neutralization of the product obtained after which bleaching is conducted in a second stage whereby a light colored acid sulfonation product is obtained. The acid sulfonation products thus obtained are useful in any application where compounds having surface-active properties are employed such as in washing or cleansing agents or the like.

Although the invention has been described with reference to certain preferred embodiments, it is not the intention of the applicants to be limited thereby and several obvious modifications of the novel method and composition are intended to be included within the broad scope of the invention as embodied in the following claims,

What is claimed is:

1. A continuous process for bleaching acid sulfonation products obtained by reacting alpha-sulfonated, substantially saturated fatty acid having 6 to 28 carbon atoms with an alcohol having from 1 to 20 carbon atoms, and thereafter contacting said fatty acid ester with a gaseous sulfur trioxide inert gas mixture in the absence of any solvent, said sulfur trioxide being employed in an amount of 1.1 to 1.7 mols S0 per fatty acid radical, which comprises contacting said alpha-sulfonated product having a temperature of 45 to 70 C. with a maximum of 4% by weight referred to said alpha-sulfonation product of a member selected from the group consisting of hydrogen peroxide, chlorous acid, hypochlorous acid, their salts and anhydrides, in the form of an aqueous preparation having a concentration of from 10 to 70 weight percent, in a first bleaching stage, at a temperature not exceeding 100 C., thereafter adding a neutralizing agent to the partially bleached sulfonation product in an amount wherein a 5% aqueous solution of the resultant product has a pH value of at least 4, and completing the bleaching in a second bleaching stage at a temperature of from 10 to 100 C. by contacting the neutralized product with a bleaching agent selected from the group consisting of hydrogen peroxide and hypochlorous acid.

2. Process according to claim 1 wherein said fatty acid ester starting material is composed of at least 70% of at least one member selected from the group consisting of C and C carbon atom fatty acid esters.

3. Process according to claim 1 wherein said fatty acid ester starting material is composed of at least 90% of at least one member selected from the group consisting of C and C carbon atom fatty acid esters.

4. Process according to claim 1 wherein said is employed in an amount of 1.2 to 1.5 mols per mol of fatty acid.

5. Process according to claim 1 wherein said bleaching agent employed in said first stage has a concentration of bleaching agent of from 15 to 60 weight percent.

6. Process according to claim 1 wherein said bleaching agent is employed in said first stage in the form of its suspension, the concentration thereof not exceeding 45 weight percent.

7. Process according to claim 1 wherein said bleaching agent is employed in said first stage in the form of its suspension, the concentration thereof not exceeding 35 weight percent.

8. Process according to claim 1 wherein said bleaching agent is used in said first stage in an amount equivalent to from 0.2 to 3% by weight of said alpha-sulfonation product.

9. Process according to claim 1 wherein the temperature in said first bleaching stage does not exceed 60 C.

10. Process according to claim 1 wherein the amount and concentration of the bleaching agent employed in said first stage is calculated to produce a mixture from the excess S present and the water introduced which is equivalent to 30 to 90 weight percent of sulfur trioxide.

11. Process according to claim 1 wherein the amount and concentration of the bleaching agent employed in said first stage is calculated to produce a mixture from the excess 80;; present and the water introduced which is equivalent to 40 to 85 weight percent of sulfur trioxide.

12. Process according to claim 1 wherein said neutralizing agent is added in an amount to produce a pH value of less than 11.

13. Process according to claim 1 wherein said neutralizing agent is added in an amount to produce a pH value of from 6- to 8.

14. Process according to claim 1 which comprises introducing the bleaching agent for said second stage together with said neutralizing agent.

15. Process according to claim 1 which comprises admixing the partially bleached sulfonation product from said first stage together with further quantities of acid sulfonation product to be bleached and bleaching agent, thereafter introducing said neutralizing agent and said second stage bleaching agent.

16. Process according to claim 15 which comprises removing from said mixture, prior to introduction of said neutralizing agent and second stage bleaching agent, at least a portion of the reaction heat liberated in said first bleaching stage.

References Cited UNITED STATES PATENTS 2,846,457 8/1958 Zemlin et al. 260-O 3,354,187 11/1967 Stein et al. 260-400 ALEX MAZ EL, Primary Examiner.

JAMES H. TURN-IPSEED, Assistant Examiner. 

